What other collections do you know besides HashMap that can be used?

Besides HashMap, Java has many other collections that can be used depending on the task:

• TreeMap — a map with sorted keys (by natural order or comparator).
• LinkedHashMap — maintains insertion order of elements.
• ConcurrentHashMap — a thread-safe version of HashMap for multi-threaded applications.
• HashSet — a set based on HashMap, stores unique elements.
• LinkedHashSet — a set that preserves insertion order.
• TreeSet — a set with sorted elements.

The choice of collection depends on requirements for order, performance, and thread safety.